Revision as of 19:14, 27 September 2011

Contents

Hard crash

When a hard crash occurs, you typically have no idea where the crash occurs. It is important to know the line where the crash occurs. So if you are able to reproduce the crash, restart GRAMPS with the command:

python -m trace -t src/gramps.py

This will usually generate vast terminal output and slow the system down for that, so redirecting output to a file is usually good:

python -m trace -t src/gramps.py >/tmp/trace.out

Then check the file "/tmp/trace.out" and save if needed, or redirect to somewhere else in the earlier step.

Add debug statements

GRAMPS is run with the optimize flag.

python -O gramps.py

This gives you the option of adding debug statements. You can use the __debug__ variable or the assert statement for this. This allows us to add code to GRAMPS that will be printed out when GRAMPS runs without the optimize flag:

This is useful when working in different parts, adding info output, and selecting on the command line with --debug the logger you want to see output with.

Use profiling

GRAMPS has a convenience hook to allow you to do profiling. Profiling gives an overview how many times methods are called in a code fragment and how long each one took. It helps to find performance bottlenecks.

An example usage:

Add at the top of the file you want to use profiling:

from Utils import profile

Then, suppose you want to profile a save function on one of the editors. The save is called due to a connect done in the method _connect_signals. So, change the connect to save to a new method testsave you make:

Now, in File menu, select 'Open Source', and open the source file you want to debug. Now all debug options are possible. Eg, go to a line in the file with the cursor, and click the run to line button. The debugger will run to that point, and left show you all defined local variables with their value, as well as the stack frame.

Try it!

Use gdb C debugger

With GObject introscpection, much more can go wrong on a lower level, causing C errors. For these gdb can be used. You should install some debug libraries like libglib2.0-0-dbg, python-gobject-dbg, ... .
Then, you start in a terminal gdb in the directory where gramps.py is stored with

gdb python

You should see something like:

GNU gdb (Ubuntu/Linaro 7.2-1ubuntu11) 7.2
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/bin/python...Reading symbols from /usr/lib/debug/usr/bin/python2.7...done.
done.
(gdb)

You just type now:

run gramps.py

and then navigate gramps to the segmentation fault. After that, you see something like

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5e7226b in g_type_check_value () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
(gdb)

Now you request the backtrace, to see the code that leads to the error:

(gdb) bt

which will print the backtrace. You are now ready to use your C knowledge to fix the bug!